Electrode system



Reiaued Oct. 10, 1950 23,282 ELECTRODE SYSTEM Elihu Craig Thomson, Boston, Mass.,assignor to Pliotoswitch, Incorporated, Cambridge, Mass, a corporation of Massachusetts Original No. 2,450,459, dated October 5, 1948, Serial No. 518,128, filed January 13, 1944. Application for reissue filed September 30, 1949, Se-

rial No. 118,791

14 Claims.

This invention relates to electrode systems for measuring electrical characteristics such as conductivity or dielectric constant of materials, and especially to devices which incorporate a standard on which the measurement can be based, in I addition to the measured sample itseli.

It is often desirable to measure an electrical property of a given substance under controlled conditions, quickly and yet exactly, or to compare an electric property of a given medium to the same property of a standard medium. For example, in certain arrangements for measuring the conductivity of liquids, the conductivity of a given solution of a substance or substances is compared to that of a similar solution of known concentration. Such arrangements are for example made use of in supervising the salinity of water in ships boilers. Devices of this type should also be independent of ambient temperature which might effect exact measurement of a medium which has a non-negligible temperature coeiiicient.

Some of the principal objects of the present invention are to provide an electrode system which essentially fulfills these requirements and is simple, compact, durable, reliable and inexpensive, and lends itself easily for insertion into any installation where measurements or supervision of the above-indicated type'are required.

In one aspect, the invention provides a cell which contains a standard specimen of the material in question, in such a manner that this specimen is permanently preserved, will not be chemically affected over a considerable time, and can be very easilyassociated with the detecting as well as the measuring components of installations of this type. In a further aspect, the electrode system according to the invention is so constructed that slight deviations from alignment of the electrodes will not adversely affect the ex- .actitude of operation. In still another aspect,

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue lating material, such as resilient rubber.

Fig. 1 is a characteristic section through an installation for supervising the conductivity of a liquid such as boiler feed water, incorporating an electrode system according to the invention;

Fig. 2 is a schematical elevation indicating a practical mounting for the electrode system shown in Fig. 1; and

Fig. 3 is the diagram of an electrical circuit suitable for an installation according to Fig. 1.

As shown in Fig. 1, a holder I supports an electrode unit III by means of mounting rings 2 and 3, fastened to holder I with an open cap 4; rings 2 and 3 are made of suitable compressible insu- The unit I0 comprises an outer guard or screen electrode member II in the form of a tube set into outer ring 2 and having perforations I2 which permit the flow therethrough of fluid to be tested. Within electrode I I and ring 3 is mounted a container, cartridge, or shell electrode I5 made of suitable metal and having a tubular sidewall I6 and an end closure I1. Within shell I5 is embedded in suitable insulating filling material I8, retained within shell I5 by means of an insulating cover 3|, a sealed vessel or cell II of glass, quartz or other material of low chemical activity.

Sealed into a stem 22 extending into cell II is a connector wire 23 the outer end of which is soldered or welded to the bottom I! of shell I5 whereas its inner end is similarly fastened to a tubular inner electrode 25, surrounding stem 22. Close to the inside of the wall 01' vessel 2| and coaxial toelectrode 251s arranged a second tubular electrode 26 which is connected to a wire 21 which leads by means of a suitable seal 28 through vessel II, and also through filler I8 and the cover 3| which closes shell I5. The electrodes 25, 26 may be suspended on wires 23, 21,

' respectively, or they may lit, and be supported by stem and cell wall, respectively. The electrodes as well as the lead wires are made of a metal or metal alloy of low chemical activity.

The vessel is filled, through stem I9 which is then sealed, with material of known electrical characteristics, providing a standard for measuring the corresponding characteristics of the material to be supervised. In the example herein described, the cell will be filled with feed water of known, standard concentration.

Soldered to wire 21, cartridge I5 and guard II are at A, B, C respectively, the wires ll, l2, ll of a conductor cord 45 secured to holder I in any suitable and convenient way.

The holder I may be of any suitable form, and supported in any manner convenient for the pur- Mac at hand.- By way of example, the installation of an electrode system according to the invention, within a tube conducting liquid to be supervised, and permitting withdrawal of the electrode system for inspection and exchange is shown in Figs. 1 and 2 as follows:

box ll screwed at 59 to tube I and sealing a tube II that is fastened to holder l, and carries handles I2. Cord ll may be confined within tube I from where it leads to the measuring circuit. I

By way of example, the use of an electrod systemaccording to the prescnt'invention in a Q measuring circuit will reference to Fig. 8.

The circuit shown in Fig. 3 may be supplied from a direct current line BI, 82 from which current of practically constant voltage is derived by suitable conventional means indicated by a gas-filled voltage regulator tube Tv in series with limiting resistance Rv. It is evident that, with suitable rectifying means, an alternating current supply might be used.

Alternating current for the measuring circuit is derived from a conventional electronic oscillator 0, preferably of a type which is essentially stable with frequency, connected to constant voltage supply SI, S3. The output circuit of the oscillatorcontains the primary Llp of a transiormer I] whose secondary Lls feeds into a detecting circuit with potentiometer resistor Rd, terminal wire 84 and tap N. The tap N of resistor Rd is connected to the probe contact-A. The primary Dip of a transformer Ll, which couples now be described with the detecting circuit to a measuring circuit, is 7 connected on the one side to the second probe contact 13 and on the other side to terminal 84 and the third probe contact C.

The secondary Lis of transformer Ll is on the one side connected to supply terminal BI, and on the other to cathode k3 of a rectifier tube Tr whose anode al is coupled, by means of resistor Rn to the grid g4 with condenser Cm, of a measuring amplifier tube Tm with anode at and cathode kl. Proper relation between the potentials of grid gl and cathode k4 is maintained by means of adJustable resistance Rm.

The anode at of meter tube Tm is connected to lead 83 through a meter relay coil M, if desired in series with a meter m.

Meter relay coil M actuates a switch 81 which, with the current in the anode circuit of Tm below a certain value, energizes a suitable signaling device D.

Between the probe terminals A and B is connected the,standard liquid column between cell electrodes 25 and 26, and between terminals B and C the resistance to be measured, namely the feed water column flowing between shell electrode It and guard electrode ll. shell is are of course connected through wire I3. This arrangement functions as follows:

The output energy of the oscillator applies a substantially constant voltage E, of substantially constant frequency, across points 34 and N of detecting resistor Rd, which voltage E is applied to terminals A and C. The voltage E and the voltage e between terminals C and B follow the relation C(Ix-l-lk) =rxlt', where r: is the known re- Cell'electrode ll andv 4 sistance of the standard solution in cell 2! (Fig. 2) and r; the unknown varying resistance of the fluid column in tube ll between electrodes Ii and I5. Hence,

rr+rr The standard solution with resistance r! is a solution of the same substance as is present in solution 1': and the two solutions will therefore have substantially the same temperature coefficient of resistance. The expression 1' x+ k is then independent of the temperature.

The voltage e appears between terminals B and C, and hence across transformer L5 which impresses a voltage proportionate thereto on grid g4 of tube Tm, upon rectification by tube Tr.

Accordingly, the conductivity of tube Tm will be proportionate to e and therefore to TX by the expression fected by*the temperature of the liquid in cell 2 l Milliammeter in, it properly calibrated, will directly indicate the concentration of the fluid passing through conduit II, 62.

By adJusting' magnet M for response at a selected value of e, the signaling device D will respond when the concentration exceed that permissible value. 1

It will now be understood that the standard cell need not be connected between terminals A and B, but can be connected between B and C, with the solution of unknown conductivity connected between A and B, provided that a function between E and e is maintained which is similar to that explained above with reference to Fig. 3.

If it is desired to inspect or to exchange the electrode system, pipe 8| and holder I are withdrawn by pulling handle 62 outwardly through gland 51 until holder I and unit Ill have passed gate valve 55, as shown with dotted lines in Fig. 2. The gate valve is then closed, whereupon the gland can be unscrewed at 5! and holder l conveniently removed while the flow of liquid through tubes SI and I2 is not afl'ected. After reinserting the electrode system or a new holder, the stufllngbox is screwed back onto tube 6d at 58, with holder i close to the stumng box. After tightening the seal around tube 6|. the gate valve 55 is opened and holder 1 with the electrode unit pushed into T-connector 52, into the position shown inl lg. 1.

It should be noted that the electrode cylinders II, Ii, 25 and 26 are so arranged that a slight disoccurring after the cell and the electrode unit as a whole have been calibrated.

It will now be evident that a device of the abovedescribed type may be used in a number of different ways for measuring either the conductivity ii conductive material is to be supervised, or the dielectric constant in the case 01' a nonconductive material, and that such material must not necessarily be a fluid but may for example be a powder. It will also be apparent that electrode systems as herein described may be used to measure the change of electrical characteristics 01' a substance with change in temperature and other physical conditions such as the change of conductivity of a fluid with change of illumination, or change of dielectric constant of a powder with mechanical disturbance.

It will further be apparent that standard cells as herein described can be used by themselveswithout temperature compensating arrangement.

Supposing that it is desired to measure the con-' ductivity of a fluid, the latter is introduced into the cell through stem H, which is then sealed. Wires 23 and 21 are used as test terminals of a circuit suitable for measuring a current passing through the cell. If it is desired to measure the change of conductivity or dielectric constant with change of temperature, the cell may be heated or cooled to any desired degree for example by submerging it in suitable baths.

It should be understood that the present disclosure is ior the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. An electrode system for measuring the conductivity of fluid of varying temperature, comprising in combination with a holder a probe unit insulated from and supported by said holder, said unit including an outer guard electrode adapted to pass said fluid, a container electrode located within said guard electrode and insulated'therefrom, a sealed vessel of insulating material secured in said container electrode and enclosing [being filled with] material of known electrical characteristics, a first electrode located in said therefrom, an insulated electrical conductor leading through said vessel and said container to said second electrode, and an outer tubular and per- Iorated metallic electrode surrounding and insulated from said container.

4. An electrode system for determining an elecsaid first electrode and said container electrode;

a second electrode disposed in contact with said material but spaced from said first electrode; and an electrical conductor insulated from said container leading from said second electrode to a point outside said container.

5. An electrode system according to claim 4, said guard electrode and said container electrode being tubular in shape and coazially mounted.

6. An electrode system according to claim 5, said guard electrode being perforated to permit passage of the fluid material.

7. An electrode system for determining an electrical property of fluid materials comprising: an insulating sealed vessel enclosing material of known electrical characteristics; a conductive container surrounding said vessel; a. first electrode disposed in contact with said material; an electrical connection between said first electrode and said container; a second electrode disposed in contact with said material but spaced from said first electrode; an electrical conductor insulated from said container leading from said second electrode to a point outside said container; and

vessel and means for electrically connecting said electrode to said container electrode through a wall of said vessel, a second electrode located in said vessel and spaced from said first electrode, and an electrical conductor connected to said second electrode and leading through said vessel and outside of said container electrode.

2. An electrode system for immersion into material of characteristics to be tested or supervised, comprising an insulating sealed vessel enclosing [filled with] material of known electrical characteristics, a conductive container surrounding said vessel, an electrode immersed in the material of said vessel, an electrical conductor connecting said electrode through said essel with said container, a second electrode located in said vessel and spaced from said first electrode, an insulated electrical conductor leading through said vessel and said container to said second electrode, and an outer electrode surrounding and insulated from said container.

3. An electrode system for immersion into material of characteristics to be tested or supervised, comprising an insulating tubular and hermetically sealed vessel enclosing [filled with] fluid material, a tubular metallic container coaxially surrounding said vessel, a tubular electrode immersed in the material of said vessel, an electrical conductor connecting said electrode through said vessel with said metallic container, a second tubular electrode located in said vessel and coaxially surrounding said first electrode and spaced an outer guard electrode surrounding and insulated from said container. v

8. An electrode system according to claim 7, said guard electrode and said container electrode being tubular in shape and coazially mounted.

9. An electrode system according to claim 8, said guard electrode being perforated to permit passage of the fluid material.

10. An electrode system for determining an electrical property of fluid materials comprising: a holder; a tubular guard electrode mounted on said holder and insulated therefrom; a tubular container electrode mounted coarially within said guard electrode and insulated therefrom; an insulating sealed vessel, enclosing material of known electrical characteristics, secured in said container electrode; a first electrode disposed in contact with said material; an electrical connection between said first electrode and said container electrode; a. second electrode disposed in contact with said material but spaced from said first electrode; and an electrical conductor insulated from said container leading from said second electrode to a point outside said container.

11. An electrode system according to claim 10, said guard electrode being perforated to permit passage of the .fluid material.

12. An electrode system according to claim 10, said first and second electrodes being cylindrical and coazially mounted within said vessel.

13. An electrode system for determining an electrical property of fluid materials comprising: an insulating sealed vessel enclosing material of known electrical characteristics," a conductive container electrode surrounding said vessel; a first electrode disposed in contact with said material; an electrical connection between said first amen 7 electrodeandsaidcontainer ebctrodenlsecond electrode disposed in contact with said material but spaced from said first electrode; an electrical conductor insulated from said container electrode leading from said second electrode to a point out- 5 side said container electrode; and a third electrodedisposed outside of. and spaced from, said container electrode.

14. An electrode system according to claim 13, said third electrode and said container electrode 10 being both mounted on an insulating holder.

ELIHU CRAIG THOMSON.

REFERENCES CITED The following references are of record in the 15 file of flfll patent or the original patent.

8 tmrmn sums m'mn'rs Number Number Name Date Kelley my 11, 1915 Edelmen Man 2'1, 1923 Keeler Feb. 3, 1925 Bonine Jan, 18, 1927 Andre Nov. 18, 1930 Christie June 28, 1939 De Lange et a1. Sept. 13. 1938 Coleman Feb. 23. 1943 Stuart Sept. 28, 1943 Wilson et a1 Feb. 27, 1945 FOREIGN PATENTS Country Date Germany Dee.,31, 1935 

